1. Field of the Invention
The present invention relates to a linear side emitter, a backlight system, and a liquid crystal display using the same.
2. Description of the Related Art
A liquid crystal display (LCD) is a type of flat panel display. An LCD is not a self-luminant display but rather utilizes external incident light from. A backlight system may be installed behind an LCD to irradiate light.
Backlight systems are classified as either direct light type systems or edge light type systems. Direct light type backlight systems directly irradiate light to a liquid crystal panel, where the light is emitted from light sources disposed directly below an LCD. Edge light type backlight systems transfer light, which is emitted from a light source installed at a side of a light guide panel (LGP), to a liquid crystal panel.
Direct light type backlight systems may use a light emitting diode (LED), which emits Lambertian light, as a point light source.
In direct light type backlight systems which use LEDs as point light sources, a plurality of LEDs are arranged in a 2-dimensional array. Specifically, the LEDs are aligned in a plurality of rows and columns.
Light emitted by the LEDs is diffused by a diffusing plate and the diffused light is irradiated on a liquid crystal panel. In order to prevent colored light from the LED array from appearing at the top portion of the diffusing plate, it is necessary to laterally transmit the light emitted from the LED array so that the light is incident on the diffusing plate.
FIG. 1 illustrates a conventional side emitting LED disclosed in U.S. Pat. No. 6,679,621.
Referring to FIG. 1, because the conventional side emitting LED uses a side emitter 1, Lambertian light emitted from an LED chip (not shown) with a given area can travel laterally through the side emitter 1. The side emitter 1 includes a funnel-shaped reflecting surface 3 inclined with respect to a central axis C′, a first refracting surface 5 inclined with respect to the central axis C′ to refract light reflected by the reflecting surface 3, and a second convex refracting surface 7 formed between a bottom surface 9 and the first refracting surface 5.
Light emitted by the LED array enters the side emitter 1. Light irradiated on the reflecting surface 3, inside the side emitter 1, is reflected by the reflecting surface 3. The reflected light is then transmitted laterally by the first refracting surface 5. Also, light transmitted toward the second convex refracting surface 7 in the side emitter 1 is transmitted laterally by the second refracting surface 7.
Since conventional side emitting LEDs laterally transmit light emitted by the LED chips, a side emitting LED array can also be used in direct light type backlight systems.
However, when conventional side emitting LEDs are used as point light sources, it is necessary to increase the distance between neighboring side emitting LEDs so as to sufficiently diffuse light emitted by the side emitting LED due to the large size of the side emitter 1. For example, when an LED chip emits Lambertian light in an area of 1 mm×1 mm, a gap between two neighboring side emitting LEDs should be larger than 10 mm.
This larger gap causes an increase in the thickness of the backlight system. This is because the mixing distance for producing uniform white light must be increased as the gap becomes larger.